Our dishwasher is probably over 8 years old - Frigidaire FDB61RJS0. It is used on a regular basis and for weeks after completion of the wash cycle it does not start the drying cycle.
The first part of the wash is fine and the rotary knob on the front goes around as it should until it reaches the 9 o'clock mark which is the end of wash cycle and the start of dry cycle. It will just sit there making noise until you manually turn the knob around into the dry cycle. Then it will carry on drying and finish the cycle.
I verified that the heating element gets hot in both the wash and dry cycles and I am assuming (without any dishwasher knowledge) that since the heating element is working the thermostat is good.
I have removed the little removeable center chip trap and that was clear.